Method, an arrangement, and a computer readable storage device for controlling homogeneous charge compression ignition combustion

Abstract

The invention relates to a method for operating an internal combustion engine operable in compression ignition mode, said engine comprising a fuel supply means, a piston in each cylinder causing ignition during compression ignition mode, at least one inlet and one exhaust valve, a control unit that controls the valve timing and fuel quantity, and at least one sensor for measuring an engine operation parameter. The following steps are performed when switching from spark ignition to compression ignition mode: controlling the exhaust and intake valves to perform a negative valve overlap to retain exhaust residual gas, determining a current combustion phasing timing, and correcting the combustion phasing by increasing the retained exhaust residual gas fraction by stepwise control of a combustion related parameter. The invention further relates to an arrangement and a computer readable device for controlling the combustion process.

Description

TECHNICAL FIELD [0001] The invention relates to an internal combustion engine that can be operated in homogeneous charge compression ignition combustion and spark ignition modes, as well as a method for controlling such an engine. BACKGROUND [0002] To improve thermal efficiency of gasoline internal combustion engines, lean burn is known to give enhanced thermal efficiency by reducing pumping losses and increasing ratio of specific heats. Generally speaking, lean burn is known to give low fuel consumption and low NOx emissions. There is however a limit at which an engine can be operated with a lean air / fuel mixture because of misfire and combustion instability as a result of a slow burn. Known methods to extend the lean limit include improving ignitability of the mixture by enhancing the fuel preparation, for example using atomised fuel or vaporised fuel, and increasing the flame speed by introducing charge motion and turbulence in the air / fuel mixture. Finally, combustion by auto-ig...

AI Technical Summary

Benefits of technology

[0023] By using the above methods, it is possible to correct the cycle temperature by increasing negative valve overlap. The negative valve overlap is increased by retarding IVO and / or advancing EVC.

Problems solved by technology

There is however a limit at which an engine can be operated with a lean air / fuel mixture because of misfire and combustion instability as a result of a slow burn.

In four-stroke engines, because the residual content is low, homogeneous charge compression ignition is more difficult to achieve, but can be induced by heating the intake air to a high temperature or by significantly increasing the compression ratio.

A further problem is to achieve ignition at a particular time with maintained combustion stability, while avoiding engine knocking and misfiring.

A problem in connection with homogeneous compression ignition is to control the ignition delay i.e. cylinder temperature in a way that the combustion phasing is correct at varying speed and load conditions of the engine.

As stated above, a general problem is the difficulty in controlling HCCI combustion.

Too early auto-ignition will cause the engine to knock and the engine efficiency to drop.

Knocking combustion, resulting from pressure waves caused by the combustion process, is both harmful for the engine and unpleasant for the driver / passenger of the car because of generated engine noise.

Too late auto-ignition will cause the engine cycle to cycle variations to increase.

Increased cycle-to-cycle variations can cause the engine to knock and misfire.

If a misfire occurs during HCCI operation, the engine will die when the auto-ignition is generated by trapped residual gas fraction of the previous combustion cycle.

Following a misfire, the temperature of the trapped gas will be insufficient for achieving auto-ignition in the subsequent cycle.

The extremely early combustion phasing of the first few HCCI cycles, have an impact on engine load.

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